1. Field of the Invention
The present invention relates generally to oil and gas well cementing devices and, specifically, to a well cementing valve having seal features to prevent the buildup of sand, cement particles and other contaminants which could affect the closing of the valve.
2. Description of the Prior Art
Various types of cementing valves are shown in the prior art which allow cement to be circulated through a well tubing string and out a valve into the surrounding well annulus. The term "well tubing string", as used herein, is intended to encompass pipe, tubing, liners and the like. In addition to the cementing shoe located at the lower extent of the tubing string, cementing valves were also made-up at other locations within the tubing string. These valves, which were located above the cementing shoe, were held in a closed position with shear pins to prevent premature opening while running into the hole or circulating below the valve. Once the initial cementing had been completed through the cementing shoe, a ball or plug was landed below the valve and above the shoe. Pressure would then be applied to the inside of the tubing string to shear the valve shear pins and move a spring-loaded sleeve upward to open cementing ports. The valve would remain open as long as pump pressure was applied and a spring force would be utilized to move the sleeve downward after pressure was released to close the ports. In this way, various zones or stages could be cemented in the well.
Despite the advantages of the prior art devices, such devices typically featured the spring-loaded sleeve located within a chamber on the exterior of the tool. The pressure of the flowing cement forced the piston upwardly within the chamber, thereby opening a passageway to circulate fluid into the well annulus. The problem with such designs was that sand, cement particles, or other contaminants could build-up within the annular chamber which housed the spring-loaded sleeve to prevent the moving sleeve from closing once cementing was complete.
U.S. Pat. No. 2,854,081 to Kriegel, issued Sept. 30, 1958, shows a typical prior art cementing shoe carried at the lower extent of the tubing string.
U.S. Pat. No. 1,684,551 to Manning, issued Sept. 18, 1928, shows a prior art cementing valve of the type adapted to be made up in the tubing string and featuring a spring-loaded sleeve within an annular chamber on the tool.